Synthesis of iron-rich tri-octahedral clay minerals: A review

International audienceExamples in materials science and in geology show an interest for iron-rich tri-octahedral clay mineral synthesis in large amounts and with well-defined char- acteristics. This review summarizes previously reported methods and conditions for iron-rich tri-octahedral clay mineral synthesis. Two approaches of hydrothermal synthesis have been applied: using gel or solid precursors. The most common synthesis approach is the hydrothermal synthesis using gel precursor. The synthesis of 1:1 type clay minerals were performed in reducing conditions in neutral or alkaline pH at various temperature and time ranges. The experimental conditions for 2:1 type clay mineral synthesis were in most cases similar to 1:1 type clay minerals, with in addition acidic pH and oxidizing conditions. The most commonly used methods for identifying and characterizing these minerals are X-ray diffraction, infra-red and Mössbauer spectroscopies as well as transmission electron microscopy. The thermodynamic stability of synthesized phases, as well as the reason for elements adopting a definite configuration and distribution in solid phase remain open questions

Theoretical Understanding of How Solution Properties Govern Nanofiltration Performances

Mechanisms governing transfer of ions through nanofiltration membranes are complex and it is primordial to understand how rejection and selectivity performances depend on the properties of the solution. For this purpose, a knowledge model based on a coupling between equilibrium partitioning induced by steric, electric and dielectric exclusions and transport inside pores by diffusion, convection and electro-migration is proposed to theoretically discuss the influence of solution properties on performances. After detailing the physical description of this model, the influence of ion size on rejection is firstly discussed from simulations obtained in several appropriate cases. Since electrostatic interactions are known to play a role on ion rejection, the influence of ion valence and concentration is then studied and different behaviors are brought to light depending on ions considered. Finally, the influence of confinement within nanopores on water dielectric properties and its consequences for ion separation are also addressed

Nutrient retention and release from raw exhausted grape marc biochars and an amended agricultural soil: Static and dynamic investigation

Biochar is the solid by-product of biomass thermochemical conversion via pyrolysis technique. Biochar addition to croplands as an organic amendment can improve soil properties and increase agricultural productivity. However, these positive effects depend largely on biomass feedstock and pyrolysis conditions. In this study, nutrient release from biochars derived from the slow pyrolysis of exhausted grape marc (EGM) at 300, 400 and 500 °C (EGM300, EGM400 and EGM500) was investigated through five successive leaching assays in batch mode for a total duration of 10 days. Then, nutrient leaching/retention kinetics of an agricultural soil amended with EGM500 (1% and 5% w/w) was assessed under dynamic conditions in columns. The batch experiments showed that with the exception of P, the nutrient release efficiency from the three biochars significantly increased with the increase of the number of leaching trials. The highest released amounts were observed at the fifth leaching cycle for K, Ca, P and Mg, which were about 45.5%, 41.5%, 229.5% and 48.9% higher than those registered during the first leaching assay. Regarding the column release experiments, a biochar content of 5% in the agricultural soil resulted in an increase of water leached NO3− and K+ by about 181.4% and 521.3%, respectively, and a significant reduction in Na+ and Ca2＋ transport as compared to unamended soil. In a second phase, outcomes of column feeding with a nutrient solution showed that PO43− and NO3− retention by biochar-amended soils is low. Thus, the use of EGM biochar as a slow release biofertilizer could be considered as a promising agricultural practice and a sustainable solution for biowaste management.This work was funded by FERTICHAR, Tunisia project. FERTICHAR is funded through the ARIMNet2 (2017) Joint Call by the following funding agencies: ANR (France), HAO-DEMETER (Greece), MHESRT (Tunisia). ARIMNet2 has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no. 618127. The authors gratefully acknowledge the funding agencies for their support

Synthesis of mono- and bi-layer zeolite films on alumina substrates

AbstractBilayer zeolite films ZSM-5/ZSM-5, ZSM-5/EMC-1 and NaY/ZSM-5 were synthesized on α-alumina plates. The bottom ZSM-5 or faujasite Y (NaY) zeolite layers were obtained by direct hydrothermal synthesis or by using a seeding step followed by a secondary growth method, respectively, while the secondary growth method was used for the synthesis of all the top zeolite layers. A complete characterization of the obtained materials is proposed using various techniques, such as X-ray diffraction, scanning electron microscopy, X-ray fluorescence and nitrogen sorption measurements. Continuous and highly crystallized bi-layer zeolite films with thicknesses around 11–18 μm were obtained